BIO 182 - Human Evolution

Chordate Morphological Features

1. Pharyngeal gill slits = openings into throat

2. Dorsal hollow nerve cords

3. Notochord

4. Muscular post-anal tail

3 Chordate Subphyla

Cephalochordates

Urochordates

Vertebrates

Cephalochordates (lancelets)

Small, torpedo shaped animals with “fish-like” appearance

Urochordates (tunicates)

Marine animals that have an external coat of polysaccharide (a tunic) to cover and support body.

Vertebrates (hagfish, lampreys, sharks and rays, amphibians, mammals, reptiles)

Dorsal hollow nerve cord elaborated into the spinal cord.

What synapomorphies distinguish the monophyletic group called Vertebrate?

Vertebrae - protects spinal cord

Cranium - protects brains and sensory organs

Vertebrate brains

1. Forebrain - houses sense of smell

2. Midbrain - associated with vision

3. Hindbrain - responsible for balance and hearing

In jawed vertebrates, the hindbrain consists of enlarged regions ______ and ________ ________.

Cerebellum; Medulla oblongata

What part of the forebrain elaborated, especially in birds and mammals?

Cerebrum

The monophyletic group of amniotes were named for ________ ________.

Mammary glands (produce milk)

Milk nourishes developing young is called what?

Lactation

What traits define mammals as endotherms?

Maintain high body temps by oxidizing large amounts of food and generating heat.

Body covered with layers of hair or fur made of keratin.

When do the earliest mammals in the fossil record appear?

210 million years ago

The Primates

1. Lemurs and aye-ayes from Madagascar, galagos and pottos of Africa, and lorises of South Asia

2. Tarsiers of south Asia

3. New World monkey found in Central and South America

4. Old World monkeys found in Africa and Asia

5. Gibbons of Asian tropics

6. Hominidae (great apes)

What makes a primate?

Hands and feet that are efficient at grasping

Flattened nails instead of claws on the fingers and toes

Relatively large brains

Color vision

Complex social behavior

Extensive parental care of offspring

Forward-facing eyes - good depth perception

What makes a great ape?

Relatively large body with long arms, short legs, and no tail.

A distinct way of walking.

Bipedalism!

What distinct ways of walking occur in hominids?

Orangutans live primarily in trees, but fist-walk when on the ground

Gorillas, bonobos, and chimpanzees knuck-walk

Humans are the only living great ape that is fully bipedal, walking upright on two legs

What are the main groups of Hominins?

Ardipithecus

Australopithecus

Paranthropus

Homo

Which main group evolved first in hominins?

Ardipithecus

Where have nearly all of the oldest hominid fossils been found?

East Africa

When did the very first migrations of H. sapiens start migrating out of Africa?

300,000+ years ago

Where were the oldest hominid fossils found?

In the deserts of Chad.

How old are the Sahelanthropus tchadensis / “toumai” fossils?

6-7 million years old

What is the significance of the discovery of the “Toumai” fossils?

They lengthened the roots of the hominid family tree.

Significance of Ardipithecus ramidus / “Ardi’s”

Oldest known hominid relative as of 2009. The earliest organisms ancestral to the Homo lineage.

“Ardi’s” characteristics

Oldest intact skeleton found to date; discovered at Aramis in Ethiopia in 1994

Remains belong to a roughly 4.4 million year-old adult female

Bipedal (deduced from pelvic structure) but had grasping feet

Hand bones are very complete but do NOT suggest Ardi was a knuckle-walker.

Brain size similar to today’s common chimpanzee

Significance of Australopithecus afarensis “Lucy"

Prior to Ardi’s discover, these organisms used to be the oldest ancestors of the Homo lineage.

“Lucy’s” characteristics

Largely intact skeleton found in Ethiopia in the 1970s

Remains belong to a roughly 3.5 million year-old female that was 3’7” in height.

Bipedal (deduced from pelvic structure), but had long arms, short legs, and grasping feet.

Brain size of 450 cc was similar to that of a common chimpanzee.

Homo ergaster/erectus

Considered to be ancestral to homo erectus and homo sapiens.

“Turkana’s boy’s” Characteristics

The best-preserved remains of Homo ergaster were found near Lake Turkana in Kenya.

Remains belong to a roughly 1.6 million year-old boy that died at age 9, and would’ve been 6’ tall as an adult.

The skeleton possesses a modern face, limbs, and adult height. The site also provided evidence for advanced tool technology.

Brain size of 700-800 cc was over half the volume of Homo sapiens.

Are neaderthals ancestral to Homo sapiens?

No! They’re our cousins.

Where and when were Homo neanderthalensis discovered?

In a limestone quarry in Germany’s Neander Valley in 1856.

When did Homo neanderthalensis live?

200,000 to 27,000 years ago.

Neanderthal characteristics

Average adult males were 5’6” tall.

Short, stocky, and powerfully built with a heavy brow ridge and a receding chin.

Dig sites provided lots of evidence for tool technology and their practice of burying deceased individuals.

Significance of Homo neanderthalensis

First fossils of an extinct hominid found.

Homo spaiens may have rplaced the Neanderthals. How? Why?

Gene flow. Interbreeding between homo sapiens and neanderthals led to neaderthal DNA integrated into homo sapiens and the disappearance of neanderthals as an independent group.

Homo floresiensis / “Hobbit people” characteristics

• Lived as recently as 18,000 years ago

• Adults were only 3 feet tall

• Their 380 cc brain size was similar to “lucy” and “ardi”, yet evidence suggests that they used fire and sophisticated tools

When and where were “Hobbit people” discovered?

Discovered in 2004 on the Indonesian island of Flores.

Where and when was Homo naledi discovered?

South Africa by cavers in 2013, revealed to world 2015.

Homo naledi Characteristics

Early human with a mix of traits

Skull shape like modern human, ½ the braincase size

236,000 to 335,000 years old

Initial discover comprises 1,550 specimens of bone, representing 737 different skeletal elements and at least 15 different individuals.